Rotary impact tool and clutch therefor

ABSTRACT

This invention pertains to a rotary impact tool and a clutch therefor, wherein a motor drives a cage member within which is pivotally mounted a swinging hollow hammer member. An output shaft extends through the cage member and through the hollow hammer member and includes forward and reverse impact anvil surfaces. The hammer member is mounted to swing in respect to the cage as it rotates with the cage, and it carries forward and reverse impact jaws on its internal surface. As the clutch is driven in the forward direction by an air motor or the like, the forward impact jaw is moved in and out of the path of the anvil jaw on the output shaft by cam action and during an impact blow the inertia of the rotating hammer member acts as automatic means to hold the impact jaw in engagement with the anvil jaw. A second embodiment includes a pair of hammers arranged to simultaneously strike a pair of anvil jaws on the anvil.

United States Patent Maurer 451 May9, 1972 154] ROTARY IMPACTTOOL ANDCLUTCH 21 Appl. No.: 52,826

Related US. Application Data [63] Continuation-in-part of Ser. No.852,574, Aug. 25,

1969, abandoned.

3,552,499 l/l97l Maurer ..l73/93.5 X

Primary E.\'aminerDavid H. Brown [57] ABSTRACT This invention pertainsto a rotary impact tool and a clutch therefor, wherein a motor drives acage member within which is pivotally mounted a swinging hollow hammermember. An output shaft extends through the cage member and through thehollow hammer member and includes forward and reverse impact anvilsurfaces. The hammer member is mounted to swing in respect to the cageas it rotates with the cage, and it carries forward and reverse impactjaws on its internal surface. As the clutch is driven in the forwarddirection by an air motor or the like, the forward impact jaw is movedin and out of the path of the anvil jaw on the output shaft by camaction and during an impact blow the inertia of the rotating hammermember acts as automatic means to hold the impact jaw in engagement withthe anvil jaw. A second embodiment includes a pair of hammers arrangedto simultaneously strike a pair of anvil jaws on the anvil.

23 Claims, 9 Drawing Figures PATENTEDMAY 9mm 3.661217 sum 1 0F 2INVENTOR.

SPENCER B. MAURER P'A'TENTEDMM 91912 v sum 2 of 2 seamen B.MAURER"ATTORNEY.

ROTARY IMPACT TOOL AND CLUTCH THEREFOR This application is acontinuation-in-part of my copending application, Ser. No. 852,574,filed Aug. 25, 1969, for a Rotary Impact Tool and Clutch Therefor, nowabandoned.

This invention relates to a rotary impact wrench and clutch therefor andmore particularly to an air driven impact wrench.

A conventional rotary impact wrench mechanism is known as a swingingweight" mechanism and is disclosed in U.S. Pat. No. 2,285,638, issued toL. A. Amtsberg. This mechanism uses a pair of diametrically opposedtilting hammer dogs or members which rotate around a lobed anvil and arecammed into an impact position with the lobes or jaws on the anvil byengagement with the anvil. The hammer dogs are released by the cams onthe anvil immediately before impact and means is provided for applying adrive torque to the dogs to cause them to rotate to a disengagingposition following an impact.

This version of swinging weight" type of mechanism shown in theforegoing patent is believed to have certain disadvantages and one ofthese is that it often rebounds after impact and strikes a second blowbefore disengaging the hammer from the anvil for continued rotation.Also, this mechanism is believed to be inefficient in delivering itsblow energy to the anvil because a portion of such energy is used todisengage the hammer member, causing such member to tilt towarddisengaging position during the impact.

Another version of the swinging weight" type of mechanism is shown inUS. Pat. No. 2,580,631 to E. R. Whitledge. In this version, the anvilcarries a pair of axially and diametrically spaced lobes or jaws and apair of axially spaced hammer members are pivoted in a hammer carrier ondiametrically located pins with each hammer member being extended aroundthe anvil. It is believed that this version also has problems ofstriking a second blow following impact and of using a part of theimpact energy to cam the hammer member into disengaging position. Inaddition, in this later version, due to the location of the impactsurface in the hammer member following or lagging its pivot, the impactcreates tensional stresses in the hammer member which are less desirablethan compressive stresses.

The principal object of this invention is to provide a novel impactmechanism which either eliminates or substantially minimizes theforegoing problems and is a more efficient impact mechanism.

Another object of this invention is to provide an impact tool and clutchcombination which results in a low cost, efficient, durable tool whichis light in weight, powerful in its impacting action, and which has goodrun-down characteristics.

A further object of the invention is to provide an impact clutch with aminimum number of movable parts which are easily and inexpensivelyformed, resulting in a low cost, reliable, and durable impact tool.

Another object of the invention is to provide a clutch for an impacttool which is capable of efi'icient operation at both low and highoutput torques.

Further important objects include the following: to provide a swingingweight impact wrench mechanism having a hammer member which issubstantially free of tensional stresses during impact; to provide aswinging weight" impact wrench mechanism having a swinging hammerpivoted on a novel type of pivot; to provide a swinging weight mechanismof simplified construction which prevents the hammer from tilting towarda disengaged position during rebound following impact; to provide a moreefficient swinging weight" type of impact wrench mechanism; to provide aswinging weight mechanism that is held by centrifugal force in anvilengaging position prior to impact; to provide a swinging weight"mechanism having the center of mass of the hammer near the center ofrotation of the mechanism; and to provide a swinging weight mechanismthat strikes a balanced blow to the anvil.

An aspect of the present invention lies in the provision of a rotaryimpact tool having a housing within which a motor is mounted. The outputshaft of the tool is mounted on the housing for rotation and it includesan impact receiving anvil jaw generally radially disposed on itsperiphery. A hollow cage or carrier member is coaxially around theoutput shaft and is mounted for rotation in respect to the tool outputshaft. A rigid driving connection exists between the motor and the cagemember so that the cage member rotates with the motor. A hollow hammermember is pivotally connected in the cage member for rotation therewithas the motor drives the cage member and for angular pivotal motionrelative to the cage member about an axis offset from but parallel tothe axis of rotation of the cage member. The hammer member has an impactdelivering jaw on its inside surface located between the axes andpositioned to always lead its pivotal connection. The impact jaw ismovable into and out of the path of the impact receiving anvil todeliver an impact blow thereto. Cam means cause the angular movement ofthe impact delivering jaw into the path of the anvil jaw where it isheld by centrifugal force until impact, and the inertia of the rotatinghammer member acts to prevent the disengagement during the impact blow.Automatic means cause angular movement of the impact jaw out of the pathof the anvil jaw at the end of the impact blow. The carrier can containtwo hammers for simultaneously striking a pair of anvil jaws to delivera balanced impact torque to the output shaft.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawings, and itsscope will be pointed out in the appended claims.

With reference to the drawings:

FIG. 1 is a side view of an impact tool showing the clutch portion inlongitudinal section;

FIGS. 2, 3, 4, and 5 are sectional views taken along line A A of FIG. 1,with FIG. 2 showing the clutch in its impact position;

FIG. 3 shows the clutch in its disengaged position;

FIG. 4 shows the clutch in position to start cam engagement;

FIG. 5 shows the position of the parts at the end of the cam engagement;

FIG. 6 is a longitudinal section of a second embodiment of theinvention;

FIG. 7 is an enlarged section taken on line 77 in FIG. 6 showing thehammer in impact position; and

FIGS. 8 and 9 are sections similar to FIG. 7 on a smaller scale showingthe position of the hammer following an impact.

With reference to the drawings, and particularly to the first embodiment1 shown in FIGS. 1 to 5, reference character 10 identifies the housingfor an air driven impact wrench, the air motor of which is well known inthe art and need not be described in detail.

The output shaft 11 of the air motor is coupled through meshing splinesl2, 13 to a hollow cage or carrier member 15 which is journaled bysleeve bearing 17 on the tool power output shaft 19. The motor shaft 11is coaxially aligned with the power output shaft 19 and the cage member15 is coaxially mounted around the output shaft 19, and is mounted forrotating in respect to the output shaft 19. The cage member 15 comprisesa pair of longitudinally spaced end plates 14 joined by a pair ofdiametrically spaced longitudinally extending struts l6 joining togetherthe end plates. The rear end portion of the output shaft or spindle 19is integrally formed as an anvil carrying an anvil jaw 23 extendinggenerally radially therefrom and providing a forward impact receivingsurface 20 and a reverse impact receiving surface 21. The forward end ofoutput shaft 19 is carried by bushing 9 mounted in the forward end oftool housing 10.

Within the internal diameter of the hollow cage member 15 there is achannel 18 along one of the struts 16 in which is positioned a pivot 22,forming, in effect, a roller and socket connection. The pivot 22 is aportion of a hollow hammer member or dog 25 which is mounted around theoutput shaft 19. Thus the hammer member 25 is pivotally connected in thecage member 15 about a tilt axis formed by the pivot 22 so that itrotates with the cage member under drive from the motor output shaft 11.and additionally can move with an angular pivot motion, relative to thecage member 15, about the tilt axis offset from, but parallel to, theaxis of rotation of the cage member.

The hollow hammer member 25 has on its internal surface 26 a forwardimpact jaw or surface 27 and a reverse impact jaw or surface 28 whichare movable into and out of the path of the impact receiving surfaces20, 21 respectively, as the tool operates in the forward or reversedirection. The hammer 25 is shaped in cross-section or symmetricalhalves joined along a plane extending through the axis 22.

The operation of the mechanism is explained starting from the moment ofimpact which is shown in FIG. 2, with the forward impact jaw 27 of thecage member in a hammer blow engagement with the forward anvil surfaceof the output shaft 19. The motor output shaft 11 is directly drivingcage 15 in a clockwise direction as shown by the arrow in FIG. 3.Immediately following the impact, the hammer member tilts in acounterclockwise direction about pivot 22 until the jaws disengage asshown in FIG. 3. This tilting movement of the hammer member 25 is causedeither by inertia forces during rebound of the hammer member 25following impact or by the motor torque driving the hammer memberagainst the anvil impact surface 20 which earns the hammer membercounterclockwise. This automatic disengagement of the hammer member 25will be more fully explained later.

The cage 15 and hammer member 25 are now free from the anvil jaw 23 andaccelerate in unison in a clockwise direction about the center axis ofthe anvil until the position shown in FIG. 4 is reached, at whichposition cam engagement is about to commence. Continued forward rotationof the hammer member 25 causes the reverse impact jaw 28 on the hammermember 25 to ride up over the forward anvil impact surface 20 on theanvil jaw 23, which earns the hammer 25 back to its original, or engagedposition, where it is maintained by centrifugal force acting on thecenter of gravity of the hammer member 25.

Continued rotation of the cage 15 and hammer 25 in unison, shown by FIG.5, brings the parts back to their original positions and another impactblow is delivered. During a blow the inertia of the rotating hammermember acting on the anvil acts to prevent disengagement of the hammeruntil the momentum of both the cage and hammer member has been expended.

An advantage of this tool lies in the fact that the total kinetic energyof the motor rotor from motor shaft 11, the cage 15 and the hammermember 25 is used in each impact, since there can be no disengagingaction until the momentum of the hammer member has been dissipated. Thedisengaging torque produced by the momentum of the rotor and cage iscountered by the engaging torque created by deceleration of the hammermember. When the momentum of the rotating parts has been dissipated,disengagement can occur under the influence of the motor torque, and thecycle begins again. This action is further explained later.

When a nut is loose the tool acts to run it down without impacting untilsufficient resistance is encountered, at which point the toolautomatically commences to impact. During run-down the clutch parts arein the position shown in FIG. 2, and due to centrifugal force andfriction between the hammer and anvil jaws good run-down torque isobtained from the motor, directly through the cage member 15 to thehammer member 25, and thence directly to the tool output shaft 19.

In forward rotation the forward impact jaw 27 always leads the pivotpoint 22 during rotation so that compressive stress is set up in thehammer member between the jaw and the pivot point during an impact blow.During reverse action the same effect is achieved in reverse direction.

During reverse, or loosening action of the tool, the hammer member 25 isin impacting position, similar to FIG. 2, but with reverse impact jaw 28against reverse anvil surface 21. The impacting action is similar to theforward impacting action.

The second embodiment 30 shown in FIGS. 6 to 9 strikes a pair ofsimultaneous impacts on the anvil at diametrically spaced points todeliver a balanced impact torque to the anvil. The carrier or cage 15carries a pair of identically shaped hammer members or dogs 25 and 25spaced longitudinally in the cage 15 and pivoted on tilting axes spaceddiametrically from each other. The anvil shaft 19 carries a pair ofanvil jaws 23 and 23' located longitudinally and diametrically from eachother.

Each hammer member 25, 25 pivots on a longitudinal pin 32, 32' providingtilting axes and acting similar to the roller and socket pivot 22 inFIG. 2. In this second embodiment, the hammer member 25 carries alongitudinal groove seating on its pivot pin 32 and the pivot pin 32fits in a longitudinal internal channel extending the length of a strut16 of the cage 15. This arrangement is desirable since the pin 32 is notsubjected to shearing stresses and the hammer member 25 avoids tensionalstresses which would be present if the pin 32 extended through a closedpivot bore in the hammer member 25. The above described is also true forthe hammer member 25 and pin 32'.

Each hammer member 25, 25' engages a stop means to limit its tiltingmovement in each direction about its pin 32, 32. The hammer member 25includes a notch 33 diametrically opposite its tilt pin 32 fitting overthe opposite pin 32' and the angular extent of the notch 33 is sized toabut the pin 32' as shown in FIGS. 7 and 8 to limit the tilting movementof the hammer member 25 and prevent the hammer jaws from banging againstthe anvil at the ends of its tilting movements. The hammer member 25'includes a similar notch 33 received over the pin 32 to serve in thesame manner as a stop means.

It is believed to be worthwhile to explain the various forces acting onthis impact mechanism at various stages of its operating cycle in orderfor the reader to appreciate the benefits provided by this mechanismover the prior art. Many of these forces are shown diagrammatically inFIG. 7, which shows a hammer member 25 of the second embodiment inimpact position against the anvil jaw 23.

Prior to impact, the hammer member 25 is rotating in a clockwisedirection as shown by the arrow X about the axis CR of the carrier 15and the hammer member 25 is tilted about its tilt axis CT to offset itscenter of mass CM to the left of the rotation center CR. Due to theunbalance of the hammer member 25, a centrifugal force G is createdacting along the dotted line 36 extending through the rotating center CRand the offset center of mass CM. This centrifugal force G holds thehammer member 25 in the engagement position shown in FIG. 7 so long asthe carrier 15 rotates at a high speed.

When the hammer member 25 strikes the anvil jaw 23, it decelerates veryrapidly causing several inertia forces to act on the hammer member 25.The impact surfaces 20 and 27 are formed to impact along the radialplane indicated by the dotted line 37. The plane is located to providean impact force line 38 which extends normal to the plane 37 and islocated a short distance to the right of the tilt axis CT. The forceline 38 represents the direction of the impact forces delivered to theanvil. The force line 38 is located slightly outside of the tilt axis CTin order for the motor torque to be able to cam the hammer member 25 toa disengaged position, as shown in FIG. 9, under certain conditions ofoperation, for example, if the motor is started with the hammer member25 at rest in the position shown in FIG. 7. The moment arm for thecamming force B acting along the force line 38 about the tilt axis CT isshown as M and should be short in order that the camming torque is nottoo large. In other words, this camming action is necessary to preventthe mechanism from locking up under certain conditions but should be nogreater than necessary to accomplish this purpose. As will be explainedlater, the hammer member 25 is normally tilted to a disengaging positionby inertia forces.

During the instant ofimpact, while the hammer member 25 is deceleratingand delivering its impact energy to the anvil, in-

ertia forces caused by the deceleration act to overcome the cammingforce B and to hold the hammer member 25 against tiltingcounterclockwise to the disengaging position. This action is calledimpact lock-up" and is necessary in order for the hammer member todeliver its full blow energy to the anvil.

During deceleration, inertia forces in the hammer include a linearmotion force A acting through the center of mass CM and normal to theline 36 and towards the right to either oppose or reinforce the cammingforce B acting along the force line 38 depending upon the exact locationof the center of mass CM. As shown in FIG. 7 the force A would bereinforce camming force B.

Another inertia force is also acting on the hammer member 25 due to itsangular deceleration and this is a force couple T acting in a clockwisedirection. The force couple T is combined with the linear force A toform a resultant inertia force F acting to the right, the normal to theline 36, through the center of percussion CP. The resultant force F isequal to the linear force A and is located much further from therotation center CR, where it extends to the left of the tilt axis CT andhas a moment arm L about the tilt axis CT. Due to its location, theresultant inertia force F applies a clockwise torque on the hammermember 25 about its tilt axis CT to overcome the camming force B actingalong the force line 38. Thus, the hammer member 25 is prevented frommoving during the instant of impact. It is believed that the moment armL should be at least as long as the moment arm M for the camming forceB.

Normally, the hammer member 25 and carrier rebounds through acounterclockwise angle following impact due to the resilient nature ofthe mechanism much the same as a carpenters hammer rebounds after ablow. The angle of travel of a rebounding hammer can be quite large, forexample, as much as 120 During the rebounding travel, the motor isattempting to decelerate the hammer member and this creates an inertiaforce R acting through the center of percussion CP normal to the line 36and opposite to the impact lock-up" force F. The force R applies acounterclockwise torque on the hammer member 25 causing it to swingrapidly counterclockwise to its disengaging position as shown in FIG. 8.

After the hammer member 25 reaches the disengaged position, the force Rshifts to a new position and becomes the force H, shown in FIG. 8, whichcontinues to hold the hammer member 25 in its disengaged position whilethe cage 15 is accelerated forward in the clockwise direction. Thisaction ensures that the hammer member 25 does not strike the anvil jaw23 a second blow before rotating past the anvil jaw 23.

It is recognized that the hammer 25 probably does not have to extendcompletely around the anvil to obtain all of the advantages disclosedfor this mechanism. However, it is believed that the hammer shouldextend at least 180 around the anvil and the center of mass of thehammer should be closer to the axis of rotation than to the tilt axis ofthe hammer.

While there have been described what is at present considered to be twopreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is aimed,therefore, in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A rotary impact tool comprising, in combination, a housing, a motormounted in said housing, an output shaft mounted on said housing forrotation and including an impact receiving anvil jaw generally radiallydisposed on its --periphery, a carrier member coaxially around saidoutput shaft and mounted for rotation in respect to said output shaft,driving connection means between said motor and said carrier member forrotating said carrier member, a hammer member pivotally connected insaid carrier member for rotation therewith and for angular pivotalmotion relative thereto about an axis offset from but parallel to theaxis of rotation of said carrier member, said hammer member forclockwise impact operation having a clockwise impact delivering jaw onits inside surface located between 0 and clockwise from its pivotconnection to the carrier member, said impact jaw being movable into andout of the path of said impact receiving anvil jaw to deliver an impactblow thereto, cam means for effecting the angular pivot movement of saidimpact delivering jaw into the path of said anvil jaw in a clockwisedirection relative to said carrier member, centrifugal force created bythe proportions, mass and mass center location of said hammer memberholding said impact delivering jaw in the path of said anvil jaw untilthe delivery of said impact blow thereto, and automatic means foreffecting the angular pivot movement of said impact jaw out of the pathof said anvil jaw in a counter clockwise direction in relation to saidcarrier member after the delivery of said impact blow.

2. A rotary impact tool as set forth in claim 1 wherein said hammermember extends around said output shaft for at least 3. A rotary impacttool as set forth in claim 2 wherein said hammer member completelysurrounds said output shaft.

4. A rotary impact tool comprising, in combination, a housing, a motormounted in said housing, an output shaft mounted on said housing forrotation and including an impact receiving anvil jaw generally radiallydisposed on its periphery, a carrier member coaxially around said outputshaft and journaled for rotation in respect to said output shaft,driving connection means between said motor and said carrier member forrotating said carrier member, a hammer member pivotally connected insaid carrier member for rotation therewith and for angular pivotalmotion relative thereto about an axis offset from but parallel to theaxis of rotation of said carrier member, said hammer member having aclockwise impact jaw on its inner surface located between 0 and 90clockwise from its pivot axis to the carrier member so that when thehammer member is pivoted in a clockwise direction the clockwise impactjaw moves inwardly toward said impact receiving anvil jaw, cam means toproduce said pivot motion, and centrifugal detent means to hold saidimpact jaw in said pivoted position to mate with the anvil jaw andproduce a disengaging pivot torque on the hammer member tending to pivotit out of engagement with the anvil jaw, the inertia of said rotatinghammer member acting to prevent said disengaging motion during an impactblow.

5. A rotary impact tool comprising, in combination, a housing, a motormounted in said housing, an output shaft mounted on said housing forrotation and including an impact receiving anvil jaw having an impactreceiving surface means generally radially disposed on its periphery, acarrier member mounted for coaxial rotation about said output shaft anddriven by said motor, a hollow hammer member surrounding said anvil jawand having an inner surface with impact delivering surface meanspivotally mounted in said carrier member for rotation therewith and forangular pivotal motion relative thereto about an axis parallel to butoffset from the axis of rotation of said carrier member, said impactdelivering surface means located between 0 and 90 clockwise from saidpivot connection to the carrier member, said impact delivering surfacemeans and said impact receiving surface means so arranged that uponclockwise rotation of said carrier member said impact delivering surfacemeans contacts said impact receiving surface means to deliver aclockwise impact blow and to produce a counterclockwise pivot torque onsaid hammer member to tend to pivot said impact delivering surface meansout of engagement with said impact receiving surface means.

6. A rotary impact tool comprising, in combination, a housing, a motormounted in said housing, an output shaft mounted on said housing forrotation about an axis and including an impact receiving anvil jawgenerally radially disposed on its periphery, a carrier member coaxiallyaround said output shaft and journaled for rotation in respect to saidoutput shaft, driving connection means between said motor and saidcarrier member for rotating said carrier member, a hammer memberpivotally connected to said carrier member for rotation therewith andfor angular pivotal motion relative thereto about an axis offset frombut parallel to the said axis of rotation of said carrier member, saidhammer member including an impact delivering jaw on its inside surfacelocated within 90 of its connection to said carrier member and sopositioned that for operation of the tool in one direction said hammermember pivots relative to the carrier member in that same direction tomove said impact delivering jaw into the annular path of rotation ofsaid anvil jaw, cam means to effect said pivot motion, centrifugal forcecreated by the proportions, the mass and the mass center location ofsaid hammer member holding said impact delivering jaw in said pivotedposition to deliver an impact blow in that direction to said anvil jaw.

7. A rotary impact tool comprising, in combination, a housing, a motormounted in said housing, an output shaft mounted on said housing forrotation about an axis and including an impact receiving anvil jawgenerally radially disposed on its periphery, a carrier member coaxiallyaround said output shaft and journaled for rotation in respect to saidoutput shaft, driving connection means between said motor and saidcarrier member for rotating said carrier member, a hammer memberpivotally connected to said carrier member for rotation therewith andfor angular pivotal motion relative thereto about an axis offset frombut parallel to the said axis of rotation of said carrier member, saidhammer member including an impact delivering jaw on its inside surface,so positioned that for operation of the tool in one direction saidhammer member pivots relative to the carrier member in that saiddirection to move said impact jaw into the annular path of rotation ofsaid anvil jaw, cam means to effect said pivot motion, centrifugal forcecreated by the proportions, the mass and the mass center location ofsaid hammer member holding said hammer jaw in said pivoted positionuntil it contacts said anvil jaw directly, urging same in said directionand creating an opposite pivot torque on said hammer member, theproportions, mass and mass center location of said hammer member alsocausing inertia forces during decelleration due to an impact blowsufficient to counter the disengaging pivot motion until the momentum ofthe carrier and hammer members in said one direction is dissipated.

8. A rotary impact tool comprising, in combination, a housing, a motormounted in said housing, an output shaft mounted on said housing forrotation about an axis and including an impact receiving anvil jawgenerally radially disposed on its periphery, a carrier member coaxiallyaround said output shaft and journaled for rotation in respect to saidoutput shaft, driving connection means between said motor and saidcarrier member for rotating said carrier member, a hammer memberpivotally connected to said carrier member for rotation therewith andfor angular pivotal motion relative thereto about an axis offset frombut parallel to the said axis of rotation of said carrier member, saidhammer member extending from its pivot connection with the carriermember to substantially beyond the said axis of rotation on both sidesof the anvil so as to generally surround the anvil, and including animpact delivering jaw on its inside surface so positioned that foroperation of the tool in one direction said hammer member pivotsrelative to the carrier member in that said direction to move saidimpact jaw into the annular path of rotation of said anvil jaw tocontact said anvil jaw directly, urging said anvil jaw in said directionand creating an opposite pivot torque on said hammer member whichbecomes eflective only after the momentum of said rotating members insaid direction has been dissipated.

9. The impact tool of claim 8, wherein said hammer member isproportioned, has a mass and a mass center location which cause inertiaforces acting on said hammer member while it contacts said anvil jawduring the dissipation of said momentum to overcome said opposite pivottorque.

10. The impact tool of claim 9, wherein said hammer member proportions,mass and mass center location also cause a centrifugal force to holdsaid impact jaw in the path of said anvil jaw prior to said contactbetween said jaws.

H. A rotary impact tool comprising, in combination, a housing, a motormounted in said housing, an output shaft mounted on said housing forrotation about an axis and including an impact receiving anvil jawgenerally radially disposed on its periphery, a carrier member coaxiallyaround said output shaft and journaled for rotation in respect to saidoutput shaft, driving connection means between said motor and saidcarrier member for rotating said carrier member, a hammer memberpivotally connected to said carrier member for rotation therewith andfor angular pivotal motion relative thereto about an axis offset frombut parallel to the said axis of rotation of said carrier member, saidhammer member including an impact delivering jaw on its inside surfacecapable of being pivoted into and out of the path of the anvil jaw, cammeans to pivot said impact delivering jaw into said path, centrifugalforce holding said impact delivering jaw in said path until impact withthe anvil jaw, and cam means to pivot said impact delivering jaw out ofsaid path including impact surfaces of said hammer and anvil jaw beingshaped so that during the impact of said hammer member with said anviljaw a camming force is created acting on the hammer member tending tocause the hammer jaw to pivot outwardly to disengage from said anviljaw, and said hammer member being so positioned, proportioned and havinga mass and a mass center location which will cause the creation ofinertia forces acting on said hammer member during the interval of saidimpact until the momentum of said hammer and carrier members isdissipated, thereby overcoming said camming force and preventing saidhammer jaw from pivoting outwardly during the interval of impact, saidmass center being closer to the carrier axis than to the hammer pivotaxis.

12. A rotary impact tool comprising, in combination, a housing, a motormounted in said housing, an output shaft mounted on said housing forrotation about an axis and including an impact receiving jaw generallyradially disposed on its periphery, a carrier member coaxially aroundsaid output shaft and journaled for rotation in respect to said outputshaft, driving connection means between said motor and said carriermember for rotating said carrier member in a given direction, a hammermember pivotally connected to said carrier member for rotation therewithand for angular pivotal motion relative thereto about an axis ofisetfrom but parallel to the said axis of rotation of said carrier member,said hammer member including an impact delivering jaw on its insidesurface, said hammer member being proportioned, and having a mass and amass center location which will cause the creation of a centrifugaltorque acting on said hammer member prior to the impact of said jaws tohold said hammer jaw pivoted inwardly in position to strike said anviljaw prior to said impact and will cause the creation of inertia forcesacting on said hammer during rebound of the hammer following saidimpact, after the momentum of said rotating members in said givendirection has been dissipated, that will cause said hammer jaw to pivotoutwardly to a position where it can rotate past said anvil jaw duringfurther rotation in said given direction.

13. A rotary impact tool comprising, in combination, a housing, a motormounted in said housing, an output shaft mounted on said housing forrotation about an axis and includ ing an impact receiving anvil jawgenerally radially disposed on its periphery, a carrier member coaxiallyaround said output shaft and journaled for rotation in respect to saidoutput shaft, driving connection means between said motor and saidcarrier member for rotating said carrier member, a hammer memberpivotally connected to said carrier member for rotation therewith andfor angular pivotal motion relative thereto about an axis offset frombut parallel to the said axis of rotation of said carrier member, saidhammer member including an impact delivering jaw on its inside surface,cam means to move said impact delivering jaw inwardly into the path ofrotation of said anvil jaw, said hammer impact jaw being locatedrelative to the hammer pivot axis so that the impact between said hammerimpact delivering jaw and said anvil jaw will create compressivestresses in said hammer member between its impact delivering jaw andsaid pivot axis, said hammer member being proportioned and having a massand a mass center location which will cause the creation of acentrifugal torque acting on said hammer member prior to the impactbetween said impact jaws to hold said hammer jaw pivoted inwardly inposition to strike said impact.

14. The wrench mechanism of claim 13 wherein said hammer member extendsaround said anvil over an angle of at least 170.

15. The wrench mechanism of claim 13 wherein said hammer member extendscompletely around said anvil.

16. The wrench mechanism of claim 13 wherein the mass center of saidhammer member is closer to the axis of said carrier member than to saidpivot axis of said hammer member.

17. The wrench mechanism of claim 13 wherein the impact surfaces of saidhammer jaw and anvil jaw are shaped so that during the impact of saidhammer jaw with said anvil jaw a camming force is created acting on thehammer member tending to cause its jaw to pivot outwardly to disengagesaid jaw during said impact, and said hammer member being alsoproportioned and having a mass and a mass center location which willcause the creation of inertia forces acting on said hammer member duringthe interval of said impact that will overcome said camming force andwill prevent said hammer member from pivoting outwardly during theinterval of impact.

18. The wrench mechanism of claim 13 wherein said hammer is positioned,proportioned and having a mass and a mass center location that willcause the creation of inertia forces acting on said hammer duringrebound of the hammer following the impact of said impact surfaces thatwill cause said hammer to tilt outward to a position where it can rotatepast said anvil jaw during further forward rotation.

19. The wrench mechanism of claim 13 wherein a pair of said anvil jawsare mounted on said output shaft and angularly and longitudinally spacedfrom each other; and a pair of said hammer members is pivoted in saidcarrier member in an angular and longitudinal spaced relationship andarranged to impact simultaneously with said anvil jaws.

20. The wrench mechanism of claim 19 wherein said anvil jaws areangularly spaced 180 from each other.

21. A rotary impact tool comprising, in combination, a housing, a motormounted in said housing, an output shaft mounted on said housing forrotation about an axis and including an impact receiving anvil jawgenerally radially disposed on its periphery, a carrier member coaxiallyaround said output shaft and journaled for rotation in respect to saidoutput shaft, driving connection means between said motor and saidcarrier member for rotation said carrier member as said motor isrotating, a hammer member pivotally connected to said carrier member forrotation therewith and for angular pivotal motion relative thereto aboutan axis offset from but parallel to the said axis of rotation of saidcarrier member, said hammer member including an impact delivering jaw onits inside surface located within of its pivot connection on saidcarrier member and so positioned that for operation of the tool in onedirection said hammer member pivots relative to the carrier member inthat same direction to move said impact delivering jaw into the annularpath of rotation of said anvil jaw to deliver an impact blow in thatdirection, and cam means on said hammer member located and adapted toengage said anvil jaw to pivot said impact delivering jaw into the pathof said anvil jaw at least 90 prior to the delivery of said impact blow,said hammer and anvil jaw allowing said impact delivering jaw to remainin the path of said anvil jaw while said hammer member rotates throughsaid 90 angle ending at the delivery of said impact blow.

22. The rotary impact tool of claim 21 wherein said hammer memberextends at least l 70 around said output shaft.

23. The rotary impact tool of claim 21 wherein said cam means on saidhammer member is disengaged from said anvil jaw for at least the last 90prior to striking the impact blow.

1. A rotary impact tool comprising, in combination, a housing, a motormounted in said housing, an output shaft mounted on said housing forrotation and including an impact receiving anvil jaw generally radiallydisposed on its periphery, a carrier member coaxially around said outputshaft and mounted for rotation in respect to said output shaft, drivingconnection means between said motor and said carrier member for rotatingsaid carrier member, a hammer member pivotally connected in said carriermember for rotation therewith and for angular pivotal motion relativethereto about an axis offset from but parallel to the axis of rotationof said carrier member, said hammer member for clockwise impactoperation having a clockwise impact delivering jaw on its inside surfacelocated between 0* and 90* clockwise from its pivot connection to thecarrier member, said impact jaw being movable into and out of the pathof said impact receiving anvil jaw to deliver an impact blow thereto,cam means for effecting the angular pivot movement of said impactdelivering jaw into the path of said anvil jaw in a clockwise directionrelative to said carrier member, centrifugal force created by theproportions, mass and mass center location of said hammer member holdingsaid impact delivering jaw in the path of said anvil jaw until thedelivery of said impact blow thereto, and automatic means for effectingthe angular pivot movement of said impact jaw out of the path of saidanvil jaw in a counter clockwise direction in relation to said carriermember after the delivery of said impact blow.
 2. A rotary impact toolas set forth in claim 1 wherein said hammer member extends around saidoutput shaft for at least 170*.
 3. A rotary impact tool as set forth inclaim 2 wherein said hammer member completely surrounds said outputshaft.
 4. A rotary impact tool comprising, in combination, a housing, amotor mounted in said housing, an output shaft mounted on said housingfor rotation and including an impact receiving anvil jaw generallyradially disposed on its periphery, a carrier member coaxially arouNdsaid output shaft and journaled for rotation in respect to said outputshaft, driving connection means between said motor and said carriermember for rotating said carrier member, a hammer member pivotallyconnected in said carrier member for rotation therewith and for angularpivotal motion relative thereto about an axis offset from but parallelto the axis of rotation of said carrier member, said hammer memberhaving a clockwise impact jaw on its inner surface located between 0*and 90* clockwise from its pivot axis to the carrier member so that whenthe hammer member is pivoted in a clockwise direction the clockwiseimpact jaw moves inwardly toward said impact receiving anvil jaw, cammeans to produce said pivot motion, and centrifugal detent means to holdsaid impact jaw in said pivoted position to mate with the anvil jaw andproduce a disengaging pivot torque on the hammer member tending to pivotit out of engagement with the anvil jaw, the inertia of said rotatinghammer member acting to prevent said disengaging motion during an impactblow.
 5. A rotary impact tool comprising, in combination, a housing, amotor mounted in said housing, an output shaft mounted on said housingfor rotation and including an impact receiving anvil jaw having animpact receiving surface means generally radially disposed on itsperiphery, a carrier member mounted for coaxial rotation about saidoutput shaft and driven by said motor, a hollow hammer membersurrounding said anvil jaw and having an inner surface with impactdelivering surface means pivotally mounted in said carrier member forrotation therewith and for angular pivotal motion relative thereto aboutan axis parallel to but offset from the axis of rotation of said carriermember, said impact delivering surface means located between 0* and 90*clockwise from said pivot connection to the carrier member, said impactdelivering surface means and said impact receiving surface means soarranged that upon clockwise rotation of said carrier member said impactdelivering surface means contacts said impact receiving surface means todeliver a clockwise impact blow and to produce a counterclockwise pivottorque on said hammer member to tend to pivot said impact deliveringsurface means out of engagement with said impact receiving surfacemeans.
 6. A rotary impact tool comprising, in combination, a housing, amotor mounted in said housing, an output shaft mounted on said housingfor rotation about an axis and including an impact receiving anvil jawgenerally radially disposed on its periphery, a carrier member coaxiallyaround said output shaft and journaled for rotation in respect to saidoutput shaft, driving connection means between said motor and saidcarrier member for rotating said carrier member, a hammer memberpivotally connected to said carrier member for rotation therewith andfor angular pivotal motion relative thereto about an axis offset frombut parallel to the said axis of rotation of said carrier member, saidhammer member including an impact delivering jaw on its inside surfacelocated within 90* of its connection to said carrier member and sopositioned that for operation of the tool in one direction said hammermember pivots relative to the carrier member in that same direction tomove said impact delivering jaw into the annular path of rotation ofsaid anvil jaw, cam means to effect said pivot motion, centrifugal forcecreated by the proportions, the mass and the mass center location ofsaid hammer member holding said impact delivering jaw in said pivotedposition to deliver an impact blow in that direction to said anvil jaw.7. A rotary impact tool comprising, in combination, a housing, a motormounted in said housing, an output shaft mounted on said housing forrotation about an axis and including an impact receiving anvil jawgenerally radially disposed on its periphery, a carrier member coaxiallyaround said output shaft and journaled for rotation in rEspect to saidoutput shaft, driving connection means between said motor and saidcarrier member for rotating said carrier member, a hammer memberpivotally connected to said carrier member for rotation therewith andfor angular pivotal motion relative thereto about an axis offset frombut parallel to the said axis of rotation of said carrier member, saidhammer member including an impact delivering jaw on its inside surface,so positioned that for operation of the tool in one direction saidhammer member pivots relative to the carrier member in that saiddirection to move said impact jaw into the annular path of rotation ofsaid anvil jaw, cam means to effect said pivot motion, centrifugal forcecreated by the proportions, the mass and the mass center location ofsaid hammer member holding said hammer jaw in said pivoted positionuntil it contacts said anvil jaw directly, urging same in said directionand creating an opposite pivot torque on said hammer member, theproportions, mass and mass center location of said hammer member alsocausing inertia forces during decelleration due to an impact blowsufficient to counter the disengaging pivot motion until the momentum ofthe carrier and hammer members in said one direction is dissipated.
 8. Arotary impact tool comprising, in combination, a housing, a motormounted in said housing, an output shaft mounted on said housing forrotation about an axis and including an impact receiving anvil jawgenerally radially disposed on its periphery, a carrier member coaxiallyaround said output shaft and journaled for rotation in respect to saidoutput shaft, driving connection means between said motor and saidcarrier member for rotating said carrier member, a hammer memberpivotally connected to said carrier member for rotation therewith andfor angular pivotal motion relative thereto about an axis offset frombut parallel to the said axis of rotation of said carrier member, saidhammer member extending from its pivot connection with the carriermember to substantially beyond the said axis of rotation on both sidesof the anvil so as to generally surround the anvil, and including animpact delivering jaw on its inside surface so positioned that foroperation of the tool in one direction said hammer member pivotsrelative to the carrier member in that said direction to move saidimpact jaw into the annular path of rotation of said anvil jaw tocontact said anvil jaw directly, urging said anvil jaw in said directionand creating an opposite pivot torque on said hammer member whichbecomes effective only after the momentum of said rotating members insaid direction has been dissipated.
 9. The impact tool of claim 8,wherein said hammer member is proportioned, has a mass and a mass centerlocation which cause inertia forces acting on said hammer member whileit contacts said anvil jaw during the dissipation of said momentum toovercome said opposite pivot torque.
 10. The impact tool of claim 9,wherein said hammer member proportions, mass and mass center locationalso cause a centrifugal force to hold said impact jaw in the path ofsaid anvil jaw prior to said contact between said jaws.
 11. A rotaryimpact tool comprising, in combination, a housing, a motor mounted insaid housing, an output shaft mounted on said housing for rotation aboutan axis and including an impact receiving anvil jaw generally radiallydisposed on its periphery, a carrier member coaxially around said outputshaft and journaled for rotation in respect to said output shaft,driving connection means between said motor and said carrier member forrotating said carrier member, a hammer member pivotally connected tosaid carrier member for rotation therewith and for angular pivotalmotion relative thereto about an axis offset from but parallel to thesaid axis of rotation of said carrier member, said hammer memberincluding an impact delivering jaw on its inside surface capable ofbeing pivoted into and out of the path of the anvil jaw, cam means topivot said impact Delivering jaw into said path, centrifugal forceholding said impact delivering jaw in said path until impact with theanvil jaw, and cam means to pivot said impact delivering jaw out of saidpath including impact surfaces of said hammer and anvil jaw being shapedso that during the impact of said hammer member with said anvil jaw acamming force is created acting on the hammer member tending to causethe hammer jaw to pivot outwardly to disengage from said anvil jaw, andsaid hammer member being so positioned, proportioned and having a massand a mass center location which will cause the creation of inertiaforces acting on said hammer member during the interval of said impactuntil the momentum of said hammer and carrier members is dissipated,thereby overcoming said camming force and preventing said hammer jawfrom pivoting outwardly during the interval of impact, said mass centerbeing closer to the carrier axis than to the hammer pivot axis.
 12. Arotary impact tool comprising, in combination, a housing, a motormounted in said housing, an output shaft mounted on said housing forrotation about an axis and including an impact receiving jaw generallyradially disposed on its periphery, a carrier member coaxially aroundsaid output shaft and journaled for rotation in respect to said outputshaft, driving connection means between said motor and said carriermember for rotating said carrier member in a given direction, a hammermember pivotally connected to said carrier member for rotation therewithand for angular pivotal motion relative thereto about an axis offsetfrom but parallel to the said axis of rotation of said carrier member,said hammer member including an impact delivering jaw on its insidesurface, said hammer member being proportioned, and having a mass and amass center location which will cause the creation of a centrifugaltorque acting on said hammer member prior to the impact of said jaws tohold said hammer jaw pivoted inwardly in position to strike said anviljaw prior to said impact and will cause the creation of inertia forcesacting on said hammer during rebound of the hammer following saidimpact, after the momentum of said rotating members in said givendirection has been dissipated, that will cause said hammer jaw to pivotoutwardly to a position where it can rotate past said anvil jaw duringfurther rotation in said given direction.
 13. A rotary impact toolcomprising, in combination, a housing, a motor mounted in said housing,an output shaft mounted on said housing for rotation about an axis andincluding an impact receiving anvil jaw generally radially disposed onits periphery, a carrier member coaxially around said output shaft andjournaled for rotation in respect to said output shaft, drivingconnection means between said motor and said carrier member for rotatingsaid carrier member, a hammer member pivotally connected to said carriermember for rotation therewith and for angular pivotal motion relativethereto about an axis offset from but parallel to the said axis ofrotation of said carrier member, said hammer member including an impactdelivering jaw on its inside surface, cam means to move said impactdelivering jaw inwardly into the path of rotation of said anvil jaw,said hammer impact jaw being located relative to the hammer pivot axisso that the impact between said hammer impact delivering jaw and saidanvil jaw will create compressive stresses in said hammer member betweenits impact delivering jaw and said pivot axis, said hammer member beingproportioned and having a mass and a mass center location which willcause the creation of a centrifugal torque acting on said hammer memberprior to the impact between said impact jaws to hold said hammer jawpivoted inwardly in position to strike said impact.
 14. The wrenchmechanism of claim 13 wherein said hammer member extends around saidanvil over an angle of at least 170*.
 15. The wrench mechanism of claim13 wherein said hammer member extends completely around said anvil. 16.The wrench mechanism of claim 13 wherein the mass center of said hammermember is closer to the axis of said carrier member than to said pivotaxis of said hammer member.
 17. The wrench mechanism of claim 13 whereinthe impact surfaces of said hammer jaw and anvil jaw are shaped so thatduring the impact of said hammer jaw with said anvil jaw a camming forceis created acting on the hammer member tending to cause its jaw to pivotoutwardly to disengage said jaw during said impact, and said hammermember being also proportioned and having a mass and a mass centerlocation which will cause the creation of inertia forces acting on saidhammer member during the interval of said impact that will overcome saidcamming force and will prevent said hammer member from pivotingoutwardly during the interval of impact.
 18. The wrench mechanism ofclaim 13 wherein said hammer is positioned, proportioned and having amass and a mass center location that will cause the creation of inertiaforces acting on said hammer during rebound of the hammer following theimpact of said impact surfaces that will cause said hammer to tiltoutward to a position where it can rotate past said anvil jaw duringfurther forward rotation.
 19. The wrench mechanism of claim 13 wherein apair of said anvil jaws are mounted on said output shaft and angularlyand longitudinally spaced from each other; and a pair of said hammermembers is pivoted in said carrier member in an angular and longitudinalspaced relationship and arranged to impact simultaneously with saidanvil jaws.
 20. The wrench mechanism of claim 19 wherein said anvil jawsare angularly spaced 180* from each other.
 21. A rotary impact toolcomprising, in combination, a housing, a motor mounted in said housing,an output shaft mounted on said housing for rotation about an axis andincluding an impact receiving anvil jaw generally radially disposed onits periphery, a carrier member coaxially around said output shaft andjournaled for rotation in respect to said output shaft, drivingconnection means between said motor and said carrier member for rotationsaid carrier member as said motor is rotating, a hammer member pivotallyconnected to said carrier member for rotation therewith and for angularpivotal motion relative thereto about an axis offset from but parallelto the said axis of rotation of said carrier member, said hammer memberincluding an impact delivering jaw on its inside surface located within90* of its pivot connection on said carrier member and so positionedthat for operation of the tool in one direction said hammer memberpivots relative to the carrier member in that same direction to movesaid impact delivering jaw into the annular path of rotation of saidanvil jaw to deliver an impact blow in that direction, and cam means onsaid hammer member located and adapted to engage said anvil jaw to pivotsaid impact delivering jaw into the path of said anvil jaw at least 90*prior to the delivery of said impact blow, said hammer and anvil jawallowing said impact delivering jaw to remain in the path of said anviljaw while said hammer member rotates through said 90* angle ending atthe delivery of said impact blow.
 22. The rotary impact tool of claim 21wherein said hammer member extends at least 170* around said outputshaft.
 23. The rotary impact tool of claim 21 wherein said cam means onsaid hammer member is disengaged from said anvil jaw for at least thelast 90* prior to striking the impact blow.